Landmine detection is a tedious, time consuming, dangerous, and expensive task. Perhaps a hundred million landmines are presently deployed on earth, notably in underdeveloped countries which scarcely have the resources to remove them. Hence, the development of technologies which can expedite landmine removal are in demand. For instance, the United States government has initiated a “Dog's Nose Research Program” through the Defense Advanced Research Projects Agency (DARPA). The purpose of the program is to study the ability of dogs to smell and identify vapors emanating from landmines, and to develop a chemical sensor of comparable sensitivity.
Many chemical sensors that detect explosives use secondary detection to infer the presence of target analytes. In secondary detection techniques, a sequence of chemical or other events must be initiated by the analyte molecule before the change can be transduced into an electrical signal. A simple example of a secondary detection technique would be one in which the analyte of interest, such as TNT, reaches a surface where it is decomposed into nitrous or nitric oxide (NOx, a chemical reaction product). This NOx is then subsequently detected by its ability to quench an emitting material. Another secondary detection method for explosives uses fluorescently labeled antibodies. The fluorescent antibody is attached to a substrate, and when explosives attach to the substrate, the fluorescent tag is displaced, being released into a stream of water. A fluorescence detector then detects the displaced fluorescent tag downstream in the flowing water, rather than detecting the actual analyte molecule directly. Yet another method for detecting explosives is disclosed in U.S. Pat. No. 5,082,630, entitled “Fiber Optic Detector For Immuno-Testing” issued to Partin et al on Jan. 21, 1992, which discloses a method for determining the presence of specific chemicals in air by exchanging the target chemical for a fluorescently-tagged antigen that is bound to an antibody. However, these detection methods are indirectly sensing the target analyte, and each step in a secondary detection scheme lowers the overall efficiency of the detection process. Therefore, there exists a need in the art for a detector which can directly sense the presence of a target analyte, thereby improving the efficiency of detection of analyte and reducing the potential for loss and interference, thereby overcoming the disadvantages and defects of the prior art.